Method of recovering selective solvents



'units.

Patented Dec. 9, 1941 '1 1 METHOD or RECOVERING SELECTIVE SOLVENTS Bernard Sutro Greensfelder, San Francisco, and

Monroe Edward Spaght, Wilmington, Calif., assignors to Shell Development Company, San Francisco, Calif., a corporation of Delaware No Drawing. Application April 29, 1938,

Serial No. 205,014

1 Claim.

Our invention relates to the refining, improve-- ment, and purification of hydrocarbon oils by treatment with selective solvents for relatively less paraffinic constituents, and is particularly concerned with an improved method for recovering such solvents from the extraction products. This application is a continuation-in-part of our application, Serial No. 5,247, filed February 6, 1935, now Patent No. 2,162,195, dated June 13, 1939.

In accordance with the present invention the mixture or solution of hydrocarbon oil and selective solvent obtained by extracting the oil with such a selective solvent is contacted with an organic wash solvent to effect the removal of the selective solvent from the oil.

It is known to extract mineral oils with various selective solvents for non-parafilnic hydrocarbons, such as aromatic and naphthenic hydrocarbons, the portion consisting of these hydrocarbons being commonly referred to as naphthenic portion, under conditions to cause the formation of two liquid phases or layers: The constituents of greater paraffinicity are largely undissolved in the solvent, and form a rafiinate phase, containing a small quantity of the selective solvent, often contaminated with small amounts of components which it is desired to remove from the parafiinic oil, and herein designated as extract components; the naphthenic portion which dissolves in the selective solvent forms an extract phase. consisting mainly of selective solvent and dissolved naphthenic oil, but often containing also a small quantity of valuable oil of greater parafinicity which it is desired to recover therefrom. In the most usual application of this process the oil is flowed countercurrently' to the selective solvent through a countercurrent extraction zone, which may comprise a vertical column provided with suitable contact means, or it may comprise a series of mixing and settling In certain cases it has been found desirable to carry out the extraction in the presence of a second solvent for the more parafiinic hydrocarbons, such as a low boiling parafflnic hydrocarbon, particularly liquid ethane, propane, butane, or pentane, as by flowing the selective solvent and the second solvent countercurrently to one another through the extraction zone, introducing the initial oil into the counterflowing streams at an intermediate point, and withdrawing extract and raflinate phases at spaced points,

as described in the patent to van Dijck, No. 2,023,109. In this case the rafiinate phase will also contain a quantity of the second solvent, this quantity being often several times that of the raffinate oil.

Paraflinic oils obtained in this manner are less susceptible to change of viscosity upon changes cf'temperature than the original oil, this property being conveniently measured by the viscosity index. They are, therefore, more valuable for use as lubricants. Moreover, their resistance against oxidation, carbon residue, and color is usually improved by such an extraction.

Certain of these selective solvents for naphthenic hydrocarbons mayalso be employed to remove non-parafiinic constituents other than naphthenes from the oil. For example, in the treatment of used crankcase oils or oxidized oils, oxidized and oxygenated substances may be dissolved in certain selective solvents comprising hydroxy aromatic compounds, nitrogen ring compounds, aromatic aldehydes, amino-aromatic compounds, and nitro-aromatic compounds.

In such extractions of hydrocarbon oils relatively high boiling liquids are often employed as selective solvents. The quantitative recovery of the solvent from the extraction products, e. g., from the rafiinate and extract phases, necessitated by the cost of these solvents as well as by the requirement of producing oils of a high degree. of purity, has heretofore been effected primarily by distillation or by a treatment involving washing with an oil-miscible solvent like naphtha, or dilution with water, followed by a treatment which will remove the last traces of the solvent by a chemical reaction between the treating agent and the solvent. The complete removal of such high boiling solvents from the oils is generally not feasible because of the formation of decomposition, polymerization, or reaction products of the hydrocarbons and the selective solvents. These undesirable reactions result in a degradation of the color and/or other characteristics of the oil, and are difiicult to separate; a further disadvantage is the loss of selective solvent. The use of chemical treatment, necessary when washing with naphtha or water, likewise involves a loss of selective solvent.

It is an object of this invention to provide an improved process for the recovery of such selective solvent from a mixture or solution of oil and selective solvent by treatment with an organic wash solvent which islsubstantially completely miscible with the selective solvent, and is'less miscible with the oil than with the selective solvent. Another object is to provide an improved -method for treating a mixture or solution of oil and selective solvent with such an organic solvent so as to produce an oil having a composition differing from that of the oil in the mixture being treated, thereby effecting a refining or fractionating action. The first object is distinct from and may be realized apart from the second object. Other objects of the invention will be apparent from the following detailed description.

In accordance with the present invention, it was found'that the selective solvent can be effecpliasefrom an extraction as described hereto fore) to atreatment with anorganic wash solvent which is substantially completely miscible with the selective solvent under the conditions of the treatment, and is capable of -forming two liquid layers when brought into contact with mixture or solution. In this manner theselective solvent is dissolved in the wash solvent to the exclusion of all or of the major portion of the oilto form a wash solvent phase which is immiscible with the simultaneous oil phase which contains all orthe greater part of the oil. The latterphase. usually consists predominantly of oil and may contain a varying smaller amount of the Wash solvent dissolved therein. If the oil-selec tive solvent mixture is a raflinate phase containing a second solvent for the more parafiinic hy+ drocarbons, the oil phase may also contain the second solvent, unless this was separated prior to the'step of contacting the raffinate phase with the organic wash solvent.

'The. treatment with the organic wash solvent is, preferably, but not necessarily con: ducted in countercurrent. This countercurrent washing of one of the extraction phases with the organic wash solvent may be conducted ac-. cording to the methods employed in the extraction of'liquid mixtures with selective solvents, and may employ such improvements thereon as a temperature gradient described in the patent to van Dijck, No. 2,081,720; or a backwash as described in the patent to van Dijck, No. 2,081,719.

The resulting solvent phase is separated from the oil phase. The latter may, if desired, be further subjected to successive treatments as described above until all of the selective solvent has been separated therefrom. When it isdesired to recover substantially all of the oil in the oil phase, relatively large quantities of a wash solvent having low oil-miscibility should be employed, such as, for example, one to six parts by volume of organic wash solvent to one part of the oil-selective solvent mixture. While it is possible to regulate the oil-solubility of the organic wash'solvent'to a certain extent by controlling the temperature and the composition of the wash solvent (as by employing aqueous solutions of the proper concentration), the solubility will depend largely upon the composition of the oil; also, it is not always feasible to regulate the temperature at will. A certain amount of the wash solvent will, therefore, often be found in the oil'phase, and provision for its separation must be made. This can be effected by distillation, in cases'where the organic wash solvents are low boiling and chemically stable, or by the addition of water, aided, if desired, by cooling,

in the case of water miscible wash solvents, to".

render the wash solvent insoluble in the oil and cause the formation of a new oil phase and an aqueous wash solvent phase, which are separated;

The wash solvent phase, produced by treating the'oil-selective solvent mixture with the organic wash solvent, may be similarly treated to separate the wash solvent from the selective solvent, preferably by distillation, taking the wash solvent ofi overhead and leaving the selective solvent in the distillation residue, the latter being employed to extract further quantities of oil. 'In the embodiment of the invention, wherein substantially all of the oil is .recovered in the oil phase, this distillation residue will be substantially free from oil; when oil is present in the wash solvent phase, this oil will be found in the distillation residue and returned to the process t is also possible to effect a with the latter. separation by adding water and/or chilling, as

" described above for the treatment of the oil ment with the wash solvent maybe conducted so as to cause the wash solvent phase to contain appreciabie amounts of oil in addition to the wash solvent and selective solvent. This quantity of oil may, for example, be between 1 and 40% of the oil in the oil-selective solvent mixture being treated, being generally of the order of 2% when a raflinate phase is treated, and somewhat higher when an extract phase is treated. The removal of such appreciable quantities of oil in the wash solvent phase may be effected by employing a' smaller quantity of the organic wash solvent; or by employing a wash solvent having.

a higher oil-miscibility; or by operating under conditions causing a higher oil-solubility in the wash solvent, as by using a higher temperature or using a wash solvent containing less or no water; or by a combination of these expedients.

This oil in the wash solvent phaseis highly naphthenic, and will cause the oil contained in the oil layer to be more parafiinic than the oil contained in the solution or mixture being treated. This circumstance affords another advantage to the process and permits the achievement of the second object of the invention. Thus, as was pointed out heretofore, the raifinate, phase produced in the main extraction is often contaminated with small amounts. of extract components, which are less paraflinic than the raflinate oil; When such a raffinate phase is contacted with an organic wash solvent under the conditions described, above, most of these extract components are removed from the or naphthenic constituents therein can by this method be dissolved in the Wash solvent phase, causing the formation of an oil layer containing oil which is less naphthenic than the oil in the original extract phase. Bylregulating 'the solvent power and the amount of wash solvent, as described above, sufiicient' highly naphthenic oil can be thus separated inthe wash solvent to produce an oil phase containing oil of a paraffinicity intermediate to those of the rafiinate and the extract phases produced in the extraction of the initial oil with the selective solvent. This intermediate oil (as well as the oil phase .of improved paraffinicity in'the case of the treatment of a rafiinate phase as described in the preceding paragraph) may be further treated with the same or another organic wash solvent to remove selective solvent therefrom, should'such treatment be found to be necessary. In this subseconditions causing the wash solvent to be less miscible with the oil, and causing the complete removal of the selective solvent therefrom.

When it contains appreciable amounts of dissolved oil, it is often desirable to wash the wash solvent phase, containing the solution of selective solvent in the organic wash solvent, with a preferential solvent for oil which is relatively immiscible in the solvents, such as a light parafiinic hydrocarbon, like propane, butane, pentane, or light naphtha, having a boiling temperature differing from that of the oil being treated to eii'ect the removal of such oil as a second oil phase. This phase may be subjected to distillation to separate the oil solvent, and the oil thus recovered may be withdrawn as a separate prodnot; or, particularly in the case of oil recovered from the wash solvent following a treatment of a raffinate phase, it may be mixed with further quantities of initial oil to be extracted with the selective solvent. The removal of the dissolved oil from the wash solvent phase is, however, not essential when it is not desired to remove it as a separate product, because the selective solvent and wash solvent are returned to the process for the treatment of further quantities of oil.

The solvent recovery process may be applied advantageously for the recovery of any selective solvent for naphthenic hydrocarbons, and is especially useful for recovery of selective solvents which are dimcult to recover by distillation because of their low volatility (i. e., those boiling above about 150 C.) or because of their instability or reactivity under distilling conditions. Examples of such solvents are: Nitro-aromatic compounds, such as nitrobenzene and: ni-tr toluene; hydroxy-aromatic compounds, such as cresylic acid, xylenols, carvacrol, and their derivatives, such as p-chlorophenol; amino-aromatic compounds, such as o-toluidine, and xylidines; aromatic aldehydes, such as benzaldehyde, o-tolualdehyde, and isopropyl benzaldehyde; heterocyclic compounds, like furfural or nitrogen ring compounds, such as quinoline, isoquinoline, and pyrrole; and aliphatic compounds like dimethyl sulfate. They may be used either alone or in admixture with other solvents or diluents, like benzol and light aromatic SO2- soluble extracts.

We may employ as wash solvents organic liquids which have a lower solvent power for the oil than the selective solvent, and which are sub stantially completely miscible with the selective solvent, it bein preferable to use solvents which are substantially immiscible with the oil or sparingly soluble therein. It is, further, preferred to employ low boiling, water-miscible, oxygenated aliphatic substances, since these can be readily separated from the oil phase by dilution with water and can be separated from the selective solvent in the wash solvent phase by distillation. Examples of suitable wash solvents are methyl alcohol, ethyl alcohol, acetone, and acetic acid, and aqueous solutions thereof, such as, for example, 45% ethyl alcohol.

In certain extraction processes one of the separated phases may, after the removal of certain constituents by a preliminary operation, separate into two layers or phases. Thus, in the case of a double countercurrent extraction wherein cresylic acid is flowed countercurrently to a paraffmic solvent like propane and the oil is introduced into the counterfiowing streams, the propane may be removed from the rafflnate phase prior to treatment with the wash solvent; l nk causes the raflinate to separate into two liquid phases. We may in such a situation separately treat each of these ramnate layers with the organic wash solvent, or treat them together. Also, it is possible to effect a partial separation of the selective solvent from extract or raflinate phase by distillation, and subject the residual portion to treatment with the organic wash solvent. It is understood that the treatments of an extraction phase with the organic wash solvent, as specified in the claim, does not exclude the possibility of any such a preliminary treatment of the phases.

Ernample A residual oil having the properties given in the table, was extracted in batch counterourrent with cresylic acid and propane to form extract and raffinate phases, which were separated. The rafilnate phase, after flashing off the propane, separated into two liquid raffinate phases, a phase (a) predominantly oil, and a phase (1)) containing mainly cresylic acid, which were separated and separately washed twice with methyl alcohol, resulting in the complete removal of the cresylic acid from the oil, and forming oil layers A and B, respectively, and corresponding wash solvent layers, which were separated. The wash solvent layers contained small amounts of oil. The oil in the wash solvent phase from the raffinate phase (b) was recovered distilling to boil away the methyl alcohol and suiiicient cresylic acid to reduce its volume to one half. The distillation residue was mixed with 200% by volume of methyl alcohol, resulting in the separation of an oil layer BS which was separated; this was found to have the properties shown in the table;

. Oil Oil Oil 3 layer layer layer Parts by volume 13 33 Viscosity sec. Say. Univ. at

L 121 70 71 Viscosity index 36 92 85 72 Refractive index 11 1. 5258 l. 4912 1. 4945 1. 5020 boiling above C., forming a raifinate phase and an extract phase each of which contains said selective solvent, separating the phases, effecting contact between one phase and an organic wash solvent substantially completely miscible with the selective solvent and at such a temperature and in such amount that there separates from the phase being treated an additional phase which is predominantly oil which is of greater paraflinicity than the oil in said phase being treated, separating said additional phase from the remaining portion of the phase being treated, effecting contact between the remaining portion of said phase and a solvent for oil substantially immiscible with said selective solvent at such temperature and in such amount that there separates from the layer being treated a phase which is predominantly oil, and separating the phase.

BERNARD SUTRQ GREENSFELDEB. MQNRQE SEAGIIT- 

